1. Field of the Invention
This invention relates to axial flow rotary machines and, more specifically to the reduction of maximum stress concentrations in a rotor disk for such a rotor machine.
2. Description of the Prior Art
A gas turbine engine has a compression section, a combustion section and a turbine section. An annular flowpath for working medium gases extends axially through the engine. The turbine section of the engine has a rotor assembly and a stator assembly. The annular flowpath passes in alternating succession between components of the stator assembly and components of the rotor assembly. The rotor assembly includes a disk having an axis of symmetry and a plurality of rotor blades extending outwardly into the hot working medium gases. The rotor blades are in intimate contact with the hot working medium gases and are heated by these hot gases.
In modern engines, cooling air is flowed through passages on the interior of the turbine blade to remove heat from the rotor blades. Typically, the cooling air is supplied through the disk by cooling air holes. One representative cooling air hole construction is shown in U.S. Pat. No. 3,836,279 issued to Lee entitled, "Seal Means for Blade and Shroud." The disk is adapted by a blade attachment slot to receive the rotor blades. Each cooling air hole has an exit opening in the bottom of the corresponding slot. The cross section of the disk changes abruptly at the slot location. As the disk rotates in a plane perpendicular to the axis of symmetry, the rotational forces induce tangential stress in the disk material. The interruption of the uniformity of the cross-sectional area results in a large concentration of stress at the cooling air holes. This condition is particularly serious in areas of repeated loads because the material will experience fatigue failure if the maximum stress is greater than the fatigue strength associated with an acceptable low cycle fatigue life.
At present the tangential stress concentrations at the cooling air passage in the rim of the disk cause that location to be the limiting low cycle fatigue life location of the disk. Accordingly scientists and engineers are working to provide a passage for cooling air having reduced tangential stress concentrations such that the disk has an improved low cycle fatigue life.